Many modulation circuits include a modulation reference path and a feedback path from a data sampler. The modulated signals output from both the modulation reference path and the feedback path need to be aligned in time, or phase, for optimal system performance. Conventionally, the calibration process used to perform the alignment has been performed manually. Manual alignment takes time to determine the correct setting from a default setting, especially for mass production applications. Many manual alignment processes simply use a trial and error approach for determining the correct calibration settings, further increasing the time needed to perform the calibration process.
Modulation paths are tuned to different frequencies depending on the application and system components. In the digital domain, the digital components operate according to a clock frequency and any time delays introduced by the digital components are consistent, regardless of frequency. However, in the analog domain, as a signal is modulated by analog components, a time delay introduced by the analog components varies with frequency. So the actual time delay in the analog domain is dependent on the actual wavelength of the signal being modulated. As a result, determining the calibration settings to fit all frequencies is often ineffective, since the frequency of the signal is a parameter of the system.